SMTP(8) SMTP(8)
NAME
smtp, smtpd - mail transport
SYNOPSIS
upas/smtp [ -aAdfiops ] [ -b busted-mx ] ... [ -g gateway ]
[ -h host ] [ -u user ] [ .domain ] destaddr sender
rcpt-list
upas/smtpd [ -adDfrg ] [ -c certfile ] [ -h mydom ] [ -k
evilipaddr ] [ -m mailer ] [ -n netdir ]
DESCRIPTION
Smtp sends the mail message from standard input to the users
rcpt-list on the host at network address address using the
Simple Mail Transfer Protocol. The options are:
-a if the server supports PLAIN or LOGIN authentication,
authenticate to the server using a password from
factotum(4). See RFCs 3207 and 2554. This option implies
-s.
-A autistic server: don't wait for an SMTP greeting banner
but immediately send a `NOOP' command to provoke the
server into responding.
-b ignore busted-mx when trying MX hosts. May be repeated.
-d turn on debugging to standard error.
-f just filter the converted message to standard output
rather than sending it.
-g makes gateway the system to pass the message to if smtp
can't find an address nor MX entry for the destination
system.
-h use host as the local system name; it may be fully-
qualified or not. If not specified, it will default to
the contents of /dev/sysname.
-i under -a, authenticate even if we can't start TLS.
-o under -s, use TLS even if we don't know the remote sys-
tem.
-p ping: just verify that the users named in the rcpt-list
are valid users at destaddr; don't send any mail.
-s if the server supports the ESMTP extension to use TLS
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encryption, turn it on for this session. See RFC3207 for
details.
-u specify a user name to be used in authentication. The
default name is the current login id.
Finally if .domain is given, it is appended to the end of
any unqualified system names in the envelope or header.
Smtpd receives a message using the Simple Mail Transfer Pro-
tocol. Standard input and output are the protocol connec-
tion. SMTP authentication by login and cram-md5 protocols
is supported; authenticated connections are permitted to
relay.
The options are:
-a requires that all clients authenticate to be able to send
mail.
-c specifies a certificate to use for TLS. Without this
option, the capability to start TLS will not be adver-
tised.
-d turns on debugging output, with each connection's output
going to a uniquely-named file in /sys/log/smtpdb.
-D sleeps for 15 seconds usually at the start of the SMTP
dialogue; this deters some spammers. Connections from
Class A networks frequented by spammers will incur a
longer delay.
-f prevents relaying from non-trusted networks. It also
tags messages from non-trusted sites when they deliver
mail from an address in a domain we believe we represent.
-g turns on grey/white list processing. All mail is
rejected (with a retry code) unless the sender's IP
address is on the whitelist, /mail/grey/whitelist, an
append only file. Addresses can be added to the whitel-
ist by the administrator. However, the usual way for
addresses to be added is by smtpd itself. Whenever a
message is received and the sender's address isn't on the
whitelist, smtpd first looks for the file
/mail/grey/tmp/local/remote/recipient, where local and
remote are IP addresses of the local and remote systems,
respectively. If it exists and was created more than a
few minutes go, the remote address is added to the whi-
telist. If not, the file is created and the mail is
rejected with a `try again' code. The expectation is
that spammers will not retry for more than a few minutes
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and that others will.
-h specifies the receiving domain. If this flag is not
specified, the receiving domain is inferred from the host
name.
-k causes connections from the host at the IP address,
evilipaddr, to be dropped at program startup. Multiple
addresses can be specified with several -k options. This
option should be used carefully; it is intended to lessen
the effects of denial of service attacks or broken mail-
ers which continually connect. The connections are not
logged and the remote system is not notified via the pro-
tocol.
-m set the mailer to which smtpd passes a received message.
The default is /bin/upas/send.
-n specifies the name of the network directory assigned to
the incoming connection. This is used to determine the
peer IP address. If this flag is not specified, the peer
address is determined using standard input.
-p permits clients to authenticate using protocols which
transfer the password in the clear, e.g. login protocol.
This should only be used if the connection has previously
encrypted using e.g. tlssrv(8).
-r turns on forward DNS validation of non-trusted sender
address.
-s causes copies of blocked messages to be saved in a sub-
directory of /mail/queue.dump.
Smtpd is normally run by a network listener such as
listen(8). Most of the command line options are more conve-
niently specified in the smtpd configuration file stored in
/mail/lib/smtpd.conf.
SOURCE
/sys/src/cmd/upas/smtp
SEE ALSO
aliasmail(8), faces(1), filter(1), mail(1), marshal(1),
mlmgr(1), nedmail(1), qer(8), rewrite(6), send(8),
tlssrv(8), upasfs(4)
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